This invention relates to a rotary coupling.
The purpose of the invention is to provide a simple rotary coupling for use in applications where a reverse torque must not be transmitted to the driving side of the coupling. By a reverse torque it is meant a torque applied externally to the driven part of the coupling. In this regard, the actual direction of rotation, clockwise or anti-clockwise, is immaterial; the invention is concerned with rotary couplings which are not restricted as to the direction of rotation; rather, it provides a coupling in which torque is freely transmitted from the driving side to the driven side but not vice versa.
A rotary coupling, such as is known from GB 2343923, utilises coupling units carried by a driving part and seated in recesses on a driven part. As such, a driving torque can be transmitted from the driving part to the driven part through the coupling units, but the application of a reverse torque, i.e. where the driven part attempts to drive the driving part, such as in a runaway condition, causes the coupling units to move or tilt relative to their recesses, thereby engaging a fixed braking surface on the rotary coupling and locking it up.
A problem that occurs is that, on application of the reverse torque, the wedging engagement of the coupling units with the fixed braking surface tends to be instantaneous or nearly instantaneous. This can quickly lead to fatigue and damage of the components, particularly when the rotary coupling operates at high speed and/or is particularly large.
Furthermore, when the components of the coupling operate in a lubricating environment, as opposed to operating xe2x80x98dryxe2x80x99, the instantaneous or near instantaneous locking up of the coupling tends to remove the lubricant-film layer lining the fixed braking surface, leaving the surface exposed.
Another problem that becomes apparent is that of the stability of the coupling units in the direction parallel to the rotational axis of the rotary coupling. Since the coupling units can all move independently of each other, and since the recesses do not have to be particularly deep, the coupling units can become misaligned relative to each other.
The present invention seeks to overcome or mitigate these problems.
According to a first aspect of the present invention, there is provided a rotary coupling comprising a driving part and a driven part, for transmission of driving torque between them, a fixed part in which the driving and driven parts are each rotatable coaxially, and a set of coupling units carried by the driving part and seated in recesses in the driven part so as to be in torque-transmitting engagement therewith, the coupling units being juxtaposed to an annular braking surface of the fixed part, each coupling unit being free to move, with respect to the driving and driven parts, into and out of engagement with the braking surface and including a wedging part having a wedging surface and a bearing part having a bearing surface, the arrangement being such that a driving torque, applied by the driving part to the coupling units, is transmitted by the latter to the driven part without engagement of the coupling units with the braking surface; but a reverse torque, applied by the driven part to the coupling units, first moves the bearing surface of each coupling unit into non-wedging engagement with the braking surface and then moves the wedging surface into wedging engagement with the braking surface, the wedging engagement being progressive due to the bearing surface so as to progressively lock up the rotary coupling.
According to a second aspect of the present invention, there is provided a rotary coupling comprising a driving part and a driven part, for transmission of driving torque between them, a fixed part in which the driving and driven parts are each rotatable coaxially, and a set of coupling units carried by the driving part and seated in recesses in the driven part so as to be in torque-transmitting engagement therewith, each recess having a slot and each coupling unit being juxtaposed to an annular braking surface of the fixed part and having a skirt received in the slot to stabilise the coupling unit in a direction parallel to the rotational axis of the rotary coupling, each coupling unit being free to move, with respect to the driving and driven parts, into and out of engagement with the braking surface, and the arrangement being such that a driving torque, applied by the driving part to the coupling units, is transmitted by the latter to the driven part without engagement of the coupling units with the braking surface; but a reverse torque, applied by the driven part to the coupling units, progressively moves the coupling units into wedging engagement with the braking surface so as to progressively lock up the rotary coupling.
Preferably, the skirt is a close fit in the slot so that, when a reverse torque is applied to the rotary coupling, one or both sides of the slot frictionally engage the skirt to aid movement of the coupling unit into wedging engagement with the braking surface of the fixed part.
According to a third aspect of the present invention, there is provided a rotary coupling comprising a driving part and a driven part, for transmission of driving torque between them, a fixed part in which the driving and driven parts are each rotatable coaxially, and a set of coupling units carried by the driving part and seated in recesses in the driven part so as to be in torque-transmitting engagement therewith, the coupling units being juxtaposed to an annular braking surface of the fixed part, each coupling unit being free to move, with respect to the driving and driven parts, into and out of engagement with the braking surface and including a wedging part, having a wedging surface, and a pivot element which projects from the wedging surface into contact with the braking surface of the fixed part, the arrangement being such that a driving torque, applied by the driving part to the coupling units, is transmitted by the latter to the driven part without engagement of the coupling units with the braking surface; but a reverse torque, applied by the driven part to the coupling units, pivots each wedging part about its respective pivot element so that the coupling units progressively move into wedging engagement with the braking surface to progressively lock up the rotary coupling.
Preferably, the pivot element is a ball bearing spring biased towards the braking surface.
According to a fourth aspect of the present invention, there is provided a rotary coupling comprising a driving part and a driven part, for transmission of driving torque between them, a fixed part in which the driving and driven parts are each rotatable coaxially, and a set of coupling units carried by the driving part and seated in recesses in the driven part so as to be in torque-transmitting engagement therewith, the coupling units being juxtaposed to an annular braking surface of the fixed part and being free to move, with respect to the driving and driven parts, into and out of engagement with the braking surface, each coupling unit including an opening and the driven part including a corresponding pin element which is received in the said opening, the arrangement being such that a driving torque, applied by the driving part to the coupling units, is transmitted by the latter to the driven part without engagement of the coupling units with the braking surface; but a reverse torque, applied by the driven part to the coupling units, moves each coupling unit into wedging engagement with the braking surface, the wedging engagement being progressive due to the pin element aiding the movement of the coupling unit to progressively lock up the rotary coupling.
Preferably, the coupling units of the first to fourth aspects of the invention are free to move independently of each other.
The present invention will now be described, by way of example only, with reference to the accompanying drawings.